Hypostomus cochliodon

[[Hypostomus cochliodon Group]]

Introduction

With 650 species currently considered valid (Eschmeyer 2003), the Loricariidae is the most speciose family of catfishes in the world. Loricariids are typically algivorous or detritivorous, but the Hypostomus cochliodon group (formerly the genus Cochliodon Kner) and Panaque Eigenmann are unique among fishes in that they consume wood (Schaefer & Stewart 1993; Nelson et al. 1999). The H. cochliodon group and Panaque share the derived presence of large, spoon-shaped teeth; however, they are unrelated and are placed in two different tribes, the Hypostomini and the Ancistrini, respectively (Armbruster 1997; in press).

The original description of Cochliodon was by Heckel (in Kner 1853), but the genus was described in the synonymy of Hypostomus Lacépède. Eigenmann (1922) described Cheiridodus and separated the genus from Cochliodon based on the presence of a small medial tooth cusp (vs. medial cusp absent). Most loricariids have bicuspid teeth (Muller & Weber 1992), and the presence of a mesial cusp represents a plesiomorphic characteristic within the Loricariidae. Cochliodon do actually have a small mesial cusp, but this cusp is occasionally fused into the lateral cusp and visible as a darker, thicker ridge on the tooth (pers. obs.). Isbrücker (1980) recognized Cheiridodus as a synonym of Cochliodon, but did so without comment. Armbruster (1997; in press) provided a phylogeny for the species of the Hypostominae based on morphology and determined that Cochliodon is derived from Hypostomus. In addition, Montoya-Burgos et al. (1998) found Cochliodon to be related to Hypostomus based on sequences of the 12s and 16s rRNA genes, Montoya-Burgos et al. (2002) found Cochliodon to be nested within Hypostomus based on sequence data from the mitochondrial D-loop, and Zawadzki (pers comm.) has found Cochliodon to be derived from Hypostomus based on allozymes. Armbruster (1997, in press) recognized Cochliodon as a synonym of Hypostomus and refers to the species formerly in Cochliodon as the H. cochliodon group. Weber and Montoya-Burgos (2002) and Montoya-Burgos et al. (2002) also placed Cochliodon in the synonymy of Hypostomus.

The Hypostomus cochliodon group has received little attention from authors except for original species descriptions. The seven currently accepted species of the H. cochliodon group are distributed in the Orinoco, Amazon, Essequibo, Magdalena, Paraguay, and Atrato river basins and in the Lake Maracaibo basin (Lilyestrom 1984; Armbruster & Page 1997). There has only been one modern attempt to examine the species of the H. cochliodon group. Lilyestrom (1984) provides descriptions of the species of the H. cochliodon group in Venezuela, a key to all of the species of the H. cochliodon group, and places Cochliodon pospisili Schultz into the synonymy of H. hondae. The characteristics used in Lilyestrom’s key are mostly proportions and tooth counts and do not adequately separate the species of the H. cochliodon group (pers. obs.). Armbruster and Page (1997) redescribe Rhinelepis levis Pearson, and place the species in Cochliodon. Hypostomus levis is unique among the H. cochliodon group in the absence of an adipose fin. Weber and Montoya-Burgos(2002) describe H. fonchii and suggest that it is related to the H. cochliodon group; however, they present no credible evidence for this assertion and H. fonchii is not considered to be part of the H. cochliodon group in this study.

Placing Cochliodon into the synonymy of Hypostomus is further supported by two species described herein. Hypostomus hemicochliodon and H. sculpodon predominantly eat wood, but do not have spoon-shaped teeth. These species have teeth that appear to be intermediate between other Hypostomus and other species of the H. cochliodon group (Fig. 1) and also appear to eat less wood than the other species of the H. cochliodon group (pers. obs. based on gut contents). Although many other Hypostomus will occasionally consume small amounts of wood, wood only amounts to a very small fraction of the diet (pers. obs.). In this manuscript all species of the H. cochliodon group are redescribed, four new species of the H. cochliodon group are described, and distribution maps, a key, and a phylogeny for the species of the H. cochliodon group is provided.